We are continuing studies of neural mechanisms of pain and pain inhibition in the rat, focusing our attention on endogenous opiate effects on cellular activity in the periaqueductal gray matter. This region of the brain is known to play a major role in analgesia. We are also studying the epileptic properties of the endogenous, pain-inhibitory opioid, enkephalin, with micro-administration of this substance into forebrain regions of the rat. Another area under investigation is the lateral cervical nucleus. Recent anatomical evidence shows for the first time the presence of this nucleus in the rat, and we are engaged in studying the response properties of its neurons to peripheral noxious and nonnoxious stimuli.